Tunable laser

ABSTRACT

A tunable laser system is provided which includes a tunable laser. The tunable laser combines a laser with a compliant mechanism.

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 10/085,143 (Attorney Docket No. SMT-0039) filedMar. 1, 2002, entitled “Compliant Mechanism and Method of Forming Same”,which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a tunable laser.

[0004] 2. Background of the Related Art

[0005] There is a continuing need for tunable optical components forvarious applications, such as optical networking,wavelength-division-multiplexing and other telecommunicationsapplications. In particular, numerous companies are developing tunablelasers for use in such applications.

[0006] Existing technologies for tunable optical components are eithertoo costly, unreliable, or do not exhibit the performance needs forpresent and/or future systems requirements.

[0007] The above references are incorporated by reference herein whereappropriate for appropriate teachings of additional or alternativedetails, features and/or technical background.

SUMMARY OF THE INVENTION

[0008] An object of the invention is to solve at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed hereinafter.

[0009] The invention relates to a tunable laser. More particularly, theinvention relates to a tunable laser employing a compliant mechanismthat provides precise angular and longitudinal control andreconfiguration.

[0010] Additional advantages, objects, and features of the inventionwill be set forth in part in the description which follows and in partwill become apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objects and advantages of the invention may be realizedand attained as particularly pointed out in the appended claims.

[0011] Additional advantages, objects, and features of the inventionwill be set forth in part in the description which follows and in partwill become apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objects and advantages of the invention may be realizedand attained as particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

[0013]FIG. 1 is a schematic cross-sectional side view of a compliantmechanism according to an embodiment of the invention;

[0014]FIGS. 1A and 1B show a plan view of exemplary electrodes of acompliant mechanism according to an embodiment of the invention;

[0015]FIG. 2 is a schematic cross-sectional side view of a compliantmechanism according to an embodiment of the invention, showing theisland of the compliant mechanism in a tilted configuration;

[0016]FIG. 3 is a schematic side view of a tunable laser systemaccording to an embodiment of the invention;

[0017]FIG. 4 is a schematic side view of a tunable laser systemaccording to another embodiment of the invention;

[0018]FIG. 5 is a schematic side view of a tunable laser systemaccording to an additional embodiment of the invention;

[0019]FIG. 6 is a schematic side view of a tunable laser systemaccording to still another embodiment of the invention;

[0020]FIG. 7 is an explanatory diagram detailing laser operation withrespect to the invention; and

[0021]FIG. 8 is an explanatory chart comparing features of embodimentsof the present invention to current laser technologies.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0022] Most tuneable lasers available today function at power levels ofapproximately 1 to 2 milliwatts (mW). However, what is needed for mosttelecom applications is a high-power tuneable laser, more particularly,a tunable laser that can function at power levels of 20 to 50 mW. Themost popular tunable lasers are fabricated with vertical cavitysurface-emitting lasers (VCSELs), which are intrinsically low-power.Only edge-emitting laser technology is capable of the high powersnecessary for most telecom applications. However, traditionaledge-emitting lasers are fixed wavelength devices. They can be madetunable by adding external components. However, known external tuningdevices are too expensive, too fragile, or lack other desiredperformance characteristics.

[0023] High-power tunable lasers have been developed which packagetunable mirrors with edge-emitting lasers. However, these known designsare complex, fragile, and expensive. The tunable laser according to theinvention combines an off-the-shelf, edge-emitting laser with acompliant mechanism, as discussed below, producing a variablewavelength, robust high-power laser.

[0024] The optical spectrum of a laser depends on the particularcharacteristics of the optical cavity of the laser. An optical wavepropagating through the laser cavity forms a standing wave between twomirror facets of the laser. This standing wave resonates only when thecavity length L is an integer number M of half wavelengths existingbetween the two mirrors. When the standing wave resonates, laser lightis emitted at the resonant wavelength. The present invention varies thecavity length L of a laser cavity of a laser using a compliantmechanism, thereby varying the wavelength of the light emitted by thelaser.

[0025]FIGS. 3, 4, 5, and 7 each show a tunable laser system employing acompliant mechanism, according to embodiments of the invention. Each ofthese embodiments will be discussed below in turn. As stated, eachembodiment employs a compliant mechanism. A compliant mechanism isdescribed in co-pending parent U.S. patent application Ser. No.10/085,143 (Attorney Docket No. SMT-0039) filed Mar. 1, 2002, entitled“Compliant Mechanism and Method of Forming Same”, which is herebyincorporated by reference. Any of the embodiments disclosed in U.S.patent application Ser. No. 10/085,143 (Attorney Docket No. SMT-0039)can be employed to realize the apparatus and methods according to theinvention discussed herein.

[0026]FIG. 1 also shows a compliant mechanism 10 employable in thetunable lasers, according to the invention. In the compliant mechanism10 of FIG. 1, a complaint support 20 supports an optical component, suchas mirror 25. The compliant support 20 is formed of a frame 20B, anisland 20A, and a compliant member 50, which attaches the island 20A tothe frame 20B, and provides flexibility therebetween. The mirror 25,which is affixed to the island 20A of the compliant support 20, ismovable via an actuator 60, which will be further discussed hereafter.

[0027] The frame 20B and the island 20A of the compliant support 20 arepreferably formed of a generally inflexible material, preferably amaterial that is compatible with micro-electro-mechanical systemsfabrication processes, such as silicon. However, other materials,generally or partially flexible, may also be appropriate. The compliantmember 50 is formed of a flexible material, preferably a highlycompliant polymeric material, such as an elastomer. However, othermaterials may also be appropriate.

[0028] In operation, the actuator 60 can be controlled to apply a forceto the island 20A, thereby moving the island 20A, for example, as shownin FIG. 2. The compliant member 50 exerts a restoring force to theisland 20A, which tends to urge the island 20A back into alignment withthe frame 20B when the actuating force is removed. The actuator 60functions to move at least the island 20A, and can include any numberand configuration of magnetic, electrostatic, or mechanical forcetransducers.

[0029] In a preferred embodiment, the actuator 60 includes a first set40 of electrodes 40A positioned on a surface 21A of the island 20Aopposite to a surface 21B on which the mirror 25 is positioned. In onepreferred embodiment, an anti-reflection (AR) coating 45 is providedbetween the surface 21A of the island portion 20A and the electrodes40A.

[0030] The actuator 60 further includes a common electrode 35Apositioned on a surface 31A of an actuator support 30, according to anembodiment of the invention. The actuator support 30 may include a hole325 for passing source light to the mirror 25. The actuator support 30is preferably formed of a generally inflexible material, preferably amaterial that is compatible with micro-electro-mechanical systemsfabrication processes, such as silicon. However, other materials,generally or partially flexible, may also be appropriate. The complaintsupport 20 and the actuator support 30 together form compliant mechanism10, which is described in detail in U.S. patent application Ser. No.10/085,143 (Attorney Docket No. SMT-0039).

[0031]FIGS. 1A and 1B show a plan view of the electrodes 40A and 35A. Inthis embodiment, three electrodes 40A are provided on the compliantsupport 20 and one common electrode 35A is provided on the actuatorsupport 30. However, this arrangement could be reversed. Further, avariety of other configurations of electrodes which cooperativelyfunction together could be utilized.

[0032] The electrodes 40A, 35A are configured to generate anelectrostatic force when a command signal is applied thereto. Thecommand signal can be configured to create a repulsive or an attractiveelectrostatic force between the electrodes.

[0033]FIG. 3 is a schematic side view of a tunable laser system 100,according to an embodiment of the invention. The tunable laser system100 includes a tunable laser 101 formed of a compliant mechanism 110,and a laser 115, for example, a semiconductor laser, preferably mountedon a heat sink 120. As shown in FIG. 3, the laser 115 includes an activeregion 135, and a high-reflectivity (HR) coating 145, at one sidethereof.

[0034] Mirror 125 is mounted on the island 111 of the compliantmechanism 110. Mirror 125, active region 135, and HR coating 145together form a (first) laser cavity, with mirror 125 functioning as theoutput mirror of the laser cavity. By adjusting the position of mirror125, a length of the laser cavity can be varied, varying the wavelengthof light output by the tunable laser 101. A lens 130 is preferablypositioned between the laser 115 and mirror 125 to collimate the lightfrom the laser 115.

[0035] The tunable laser system 100 may include an output optical fiber150 configured to receive light output by the tunable laser 101.Additionally, the tunable laser system 100 may include a lens 140, whichfunctions to focus output light into the output optical fiber 150.

[0036] Element 132 on the island 111 may be an anti-reflective coating.Alternatively, element 132 may be a partially reflective coating. Insuch an embodiment, partially reflective coating 132, along with activeregion 135 and HR coating 145 form a second laser cavity, whilepartially reflective coating 132 and mirror 125 form a third lasercavity. The precise resonant wavelengths of the first and secondcavities can be adjusted by tuning the position of the island 111, whichtunes the position of both the mirror 125 and the partially reflectivecoating 132, respectively, similar to the embodiment of FIG. 6 discussedbelow. Because the mirror 125 and the partially reflective coating 132move together as the position of the island 111 is tuned, the resonantwavelength of the third laser cavity, formed by mirror 125 and partiallyreflective coating 132, remains substantially constant.

[0037]FIG. 4 is a schematic side view of a tunable laser system 200,according to another embodiment of the invention. The tunable lasersystem 200 of FIG. 4 is similar to the tunable laser system of FIG. 3.Similar reference numerals have been utilized to refer to similarelements, and repetitive discussion has been omitted.

[0038] The tunable laser system 200 includes a tunable laser 201. Thetunable laser 201 employs a compliant mechanism 210, and includes alaser 215, for example, a semiconductor laser, preferably mounted on aheat sink 220. As shown in FIG. 4, the laser 215 includes an activeregion 235, and a mirror 245 at one end.

[0039] The compliant mechanism 210 supports an HR mirror 225 which,together with the active region 235 and mirror 245, forms a lasercavity. By adjusting the position of the HR mirror 225, a length of thelaser cavity can be varied, thereby varying the wavelength of lightoutput by the tunable laser 201.

[0040] A lens 230 is preferably positioned between the laser 215 andmirror 225 to collimate the light from the laser 215. Additionally, thetunable laser system 200 may include a lens 240, which functions tofocus output light into an (optional) output optical fiber 250.

[0041]FIG. 5 is a schematic side view of a tunable laser system 300according to another embodiment of the invention. The tunable lasersystem 300 is similar to the tunable laser systems of FIGS. 3 and 4.Similar reference numerals have been utilized to refer to similarelements, and repetitive discussion has been omitted.

[0042] The tunable laser system 300 of FIG. 5 includes a tunable laser301 comprised of a laser 315, for example, a semiconductor laser, usedin combination with a compliant mechanism 310. The compliant mechanismof this embodiment differs from the compliant mechanism of previouslydiscussed embodiments in that the shape of HR mirror 325 supported onthe compliant mechanism 310 is adjusted to provide a desired spatialmode of the laser light 305 output by the tunable laser 301. Forexample, in this embodiment, the HR mirror 325 is curved to provide adesired spatial mode of the output laser light 325 for coupling to anoutput optical fiber 350. The curvature of the HR mirror 325 eliminatesthe need for a focusing lens. That is, the curved mirror functions tofocus the light.

[0043]FIG. 6 is a schematic side view of a tunable laser system 400,according to another embodiment of the invention. The tunable lasersystem 400 of FIG. 6 is similar to the tunable laser systems of FIGS.3-5. Similar reference numerals have been utilized to refer to similarelements, and repetitive discussion has been omitted.

[0044] The tunable laser system 400 of FIG. 6 includes a tunable laser401, for example, a semiconductor laser, which utilizes two compliantmechanism 410A and 410B. Laser 415, preferably provided on a heat sink420, is positioned between the complaint mechanism 410A and 410B. Thelaser system depicted in FIG. 6 is a double resonant cavity design. Oneresonant cavity is formed by the gap between mirror 425B and coating446. Because the length of the cavity is relatively short, the moderesonances are relatively widely spaced as shown in FIG. 7(b). Theprecise resonant wavelengths of this cavity are adjusted by tuning theposition of mirror 425B. The second cavity is formed by the gap betweencoating 446 and mirror 425A. This cavity, being longer, has more closelyspaced resonant modes, as indicated in FIG. 7(c). The precise resonantwavelength of this cavity is tuned by adjusting the position of mirror425A. The gain profile of the laser's active output is determined by thesuperposition of the spectra of the two resonant cavities with the gainprofile as shown in FIG. 7(d). If the length of the second cavity isadjusted such that the resonant wavelengths are equal to theInternational Telecommunication Union (ITU) grid, then the laser is onlycapable of outputting at those wavelengths. The length of the firstresonant cavity is adjusted to select which one of the ITU wavelengthswill rise above the gain threshold of the active medium.

[0045] The tunable laser system 400 of FIG. 7 may further include a lens440, which functions to focus light output by the tunable laser 401 intoan output optical fiber 450.

[0046]FIG. 8 is a chart comparing the present invention to current lasertechnologies. In comparison to prior art VCSELs and edge-emitting lens,the tunable laser of the present invention provides a tuning range ofapproximately 40 mm, as well as a power level of greater thanapproximately 25 mw.

[0047] The foregoing embodiments and advantages are merely exemplary andare not to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses. Thedescription of the present invention is intended to be illustrative, andnot to limit the scope of the claims. Many alternatives, modifications,and variations will be apparent to those skilled in the art. In theclaims, means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents but also equivalent structures.

What is claimed is:
 1. A tunable laser system, comprising: a laser; andat least one compliant mechanism configured to vary a wavelength oflight output by the laser.
 2. The tunable laser system according toclaim 1, wherein the laser is a semiconductor laser.
 3. The tunablelaser system according to claim 1, wherein the compliant mechanismcomprises a mirror, and varying the position of the mirror varies awavelength output by the laser.
 4. The tunable laser system according toclaim 3, wherein the compliant mechanism comprises a compliant supportto which the mirror is fixed, and at least a portion of the compliantsupport is substantially flexible.
 5. The tunable laser system accordingto claim 3, wherein the compliant mechanism comprises a compliantsupport to which the mirror is fixed, and at least a portion of thecompliant support comprises silicon, and another portion of thecompliant optical support comprises a compliant material.
 6. The tunablelaser system according to claim 5, wherein the compliant materialcomprises an elastomer.
 7. The tunable laser system according to claim3, wherein the mirror is movable by an actuator.
 8. The tunable lasersystem according to claim 7, wherein the compliant support comprises: anisland, to which the mirror is affixed; and a frame, wherein the islandand the frame are flexibly joined by a compliant member.
 9. The tunablelaser system according to claim 8, wherein at least a portion of theactuator is attached to the island.
 10. The tunable laser systemaccording to claim 8, wherein the compliant member comprises anelastomer.
 11. The tunable laser system according to claim 8, whereinthe island and the frame comprise silicon.
 12. The tunable laser systemaccording to claim 8, wherein the actuator comprises: a plurality ofelectrodes positioned on a surface of the island opposite a surface towhich the second mirror is attached; and an electrode disposed on anactuator support.
 13. The tunable laser system according to claim 12,wherein the actuator support comprises silicon.
 14. The tunable lasersystem according to claim 1, further comprising an output optical fiberinto which output light is directed.
 15. The tunable laser systemaccording to claim 14, further comprising: a lens configured to focuslight into the output optical fiber.
 16. The tunable laser systemaccording to claim 1, further comprising: a lens configured to collimatelight output by the laser.
 17. The tunable laser system according toclaim 1, wherein the compliant mechanism is positioned between the laserand an output optical fiber.
 18. The tunable laser system according toclaim 1, wherein the laser is positioned between the compliant mechanismand an output optical fiber.
 19. The tunable laser system according toclaim 3, wherein the mirror is curved.
 20. The tunable laser systemaccording to claim 19, wherein the laser is positioned between thecompliant mechanism and an output optical fiber.
 21. The tunable lasersystem according to claim 1, wherein the at least one compliantmechanism comprises two compliant mechanisms.
 22. The tunable lasersystem according to claim 21, wherein the laser is positioned betweenthe two compliant mechanisms.
 23. The tunable laser system according toclaim 22, wherein the laser comprises an anti-reflective on one end andan approximately 30% reflective coating on the other end.
 24. Thetunable laser system according to claim 21, further comprising: anoutput optical fiber positioned to receive output light.
 25. The tunablelaser system according to claim 24, further comprising: a lensconfigured to focus the output light into the output optical fiber. 26.The tunable laser system according to claim 21, wherein the twocompliant mechanisms each comprise a mirror, and wherein varying theposition of either mirror varies a wavelength output by the tunablelaser.
 27. The tunable laser system according to claim 26, wherein eachmirror is curved.
 28. The tunable laser system according to claim 1,wherein the laser comprises a first fixed mirror and an active region,and the compliant mechanism further comprises a second mirror mountedthereon, wherein a first laser cavity is formed between the first andsecond mirror, and wherein adjusting the position of the second mirrorvaries a wavelength of light output by the tunable laser.
 29. Thetunable laser system according to claim 28, wherein the compliantmechanism further comprising a partially reflective coating, wherein asecond laser cavity is formed between the partially reflective coatingand the first mirror, which is tunable by adjusting the position of thepartially reflective coating, and wherein a third laser cavity is formedbetween the partially reflective coating and the second mirror, which istunable by adjusting the position of the second mirror.
 30. A tunablelaser, comprising: a first fixed mirror; a second mirror mounted on acompliant mechanism; and an active region formed between the first andsecond mirrors.
 31. The tunable laser according to claim 20, whereinvarying the position of the second mirror varies a wavelength output bythe tunable laser.
 32. A telecommunication system comprising the tunablelaser system of claim 1.